1. Technical Field
The present invention relates in general to printed circuit card mechanical design, and in particular to printed circuit card mechanical design providing strain relief to mounted components.
2. Description of the Related Art
The conventional approach to the fabrication of large, dense multi-chip electronic packages has been the large or very large scale integrated circuit in which a single large monolithic silicon chip is used as a substrate on which all required circuits are integrated. The chip is then packaged in one of several multi-lead electronic packages. As an alternative to such single chip modules (SCM), multi-chip modules (MCM) have been developed. In a typical MCM, complex circuitry is distributed among two or more separate chips, or sub-chips. Each such sub-chip contains only a portion of the overall circuitry of the MCM and is, therefore, substantially less complex and expensive to design, prototype, build and test than the equivalent monolithic chip. Such modular designs produce circuitry components that are substantially larger then most other components mounted to a circuit board.
SCMs and MCMs are often designed as surface mounted devices, which are mounted directly on the circuit board by soldering the module's leads directly to the circuit board. Often, the soldered leads are not only providing the electrical connections from the module to the circuit board, but are the only mechanical means of anchoring or attaching the surface mounted module to the board. Unfortunately, because of the large mass of the modules and the comparatively thin circuit card cross-section underlying the module, any vibration of the module in the normal direction or rotational direction from the card, or lateral shock loads transmitted through the module into the card will cause a high level of stress in the edge and corner solder joints of the module.
Moreover, because such large microcircuit modules are highly susceptible to damage from heat generated internally, large heat sinks having small thin metal extrusions or fins are often mounted to the top of the modules. The addition of this mass of the heat sink only enhances the problem of stress and strain of the edge and corner solder joints.
This stress and strain on the modules electrical connections cause an unusually high field failure rate of the package. Therefore, it would be desirable to provide a means of module strain relief to prevent card and module vibration from causing high stress and failure to solder joints on the edge and corner joints of a many leaded surface mounted module and heat sink.